An image display device such as a liquid crystal display or a projector is provided with a high pressure mercury lamp or the like as a light source. A high pressure mercury lamp is structured such that mercury or gas is confined in a glass tube. Thus, if the temperature of the lamp excessively rises, the glass tube will explode. To prevent such a situation, image display devices that use a high pressure mercury lamp as a light source are generally provided with a cooling fan that cools the light source.
Patent Literature 1 describes a projector that has a light source; a temperature measurement means that measures the temperature in the neighborhood of the light source; a cooling fan that cools the light source; and a control section that controls voltage supplied to the cooling fan based on the temperature measured by the temperature measurement means.
The foregoing projector controls voltage supplied to the cooling fan such that the number of rotations of the cooling fan that has been set according to the measured value of the temperature is maintained.
Recent projectors that have a high pressure mercury lamp or the like as a light source are provided with an energy saving mode that the user can select so as to decrease the brightness of an image. Energy saving modes include a low power lighting mode that allows power supplied to the lamp to be decreased to around several tens of percent of the maximum power.
The foregoing low power lighting mode may be manually set up if the user does not need a high brightness image. Alternatively, when an image that the user does not watch is generated, for example, a lens shutter or the like causes a projected image to become a black image, a blue screen is displayed after an external image signal has not been input for a predetermined time, or an AV mute function is activated so as to temporarily stop displaying an image and outputting sound, the low power lighting mode may be set up along with such an image.
When the temperature of the light source in the high brightness image display state is compared with that in the low brightness image display state, it is natural that the temperature of the light source in the low brightness image display state is lower than the temperature in the high brightness image display state. In addition, since these temperatures are constant to some extent, it can be contemplated that the number of rotations of the cooling fan may be controlled based on the selected lighting mode without it being necessary to provide a temperature measurement means as described in Patent Literature 1.